A suitable prior art pump includes a pump chamber comprising first and second telescopically-slidable cylinders with the pump chamber being capable of being closed by relative displacement of the cylinders. The first cylinder is integral with the pump outlet valve and is provided at one of its ends with a circular sealing lip capable of engaging against and of sliding along the wall of the second cylinder, which second cylinder is in communication with the inside of the receptacle. When the facing edges of the two cylinders at a distance are apart from each other, the gap between the two edges allows communication to take place between the pump chamber and the inside of the receptacle. When one of the cylinders is engaged inside the other, this communication is interrupted and the pump chamber is isolated, thus providing a pump chamber which is annular in shape and which surrounds said two cylinders. Such pumps are described, for example, in French patents numbers 2 305 241 and 2 341 772 and in the corresponding U.S. Pat. No. 4,025,046. The pumps described in these patents are used without a propellant gas. They could naturally also be used with a propellant gas by ensuring that there is no communication with the outside atmosphere, i.e. that the volume of liquid expelled by the pump is not replaced by a volume of air. However, this raises the problem of inserting the propellant gas into the receptacle after the receptacle has been filled with liquid and the pump has been put into place and crimped onto the receptacle.
An object of the present invention is to make it possible to fill the volume left empty in the receptacle with the peopellant gas in a manner which is simple and reliable.
French patent number 2 407 752 describes a precompression pump atomizing a liquid, but in which no provision is made for receiving a gas under pressure in order to prevent the entry of air to replace the volume of liquid that is ejected. In this prior pump, as in the other pumps mentioned above, the outlet valve opens only when the pressure in the chamber reaches a certain value. When the pump is primed, the chamber is filled with liquid. If the volume of the chamber is reduced, then the pressure rises to a high value very quickly since the liquid is incompressible, so the valve member lifts and the liquid is expelled. However, when the pump is first used, its chamber is filled with air so reducing the volume of the chamber raises the gas pressure relatively little and the valve member does not lift. The air stagnates in the chamber and initial pump primimg is made difficult. The pump described in said patent includes means for facilitating such priming, or even for making priming possible. To this end, the second cylinder is provided with notches or projections for putting the volume of the pump chamber into communication with the inside of the receptacle when the pump is actuated to its fullest extent. Passages are thus disengaged level with the sealing lip. The cross-section of these passages is very small. They serve solely for evacuating the volume of air from the chamber. The pump position required for obtaining such evacuation must necessarily be obtained by normal manual actuation of the pump.
The present invention relates to means making it possible to insert gas into the receptacle after it has been filled with liquid, with the quantity of gas inserted being sufficient to prevent any air from entering the receptacle until all of the liquid has been expelled therefrom.